Sinpo is home to a North Korean submarine base. The third failed at launch.
Robinson is the top officer at U.S. Northern Command and the North American Aerospace Defense Command in Colorado.
Any launch of objects using ballistic missile technology is a violation of U.N. Security Council resolutions.
Japan's Chief Cabinet Secretary Yoshihide Suga described the launch as "extremely problematic" and said Tokyo had lodged a strong protest. U.S. Pacific Command's initial assessments indicate the type of missile was a KN-15 medium-range ballistic missile. We have no further comment.
Obama warned Trump before he took office that the rogue nation's nuclear program would present him with the most worrisome global challenge. When conducting nuclear and missiles tests in recent years, it has cited what it calls increasing US military threats.
"I told (President Trump) that Japan is watching closely how China will cope with this North Korean issue", Abe told reporters after the 35-minute conversation.
Though the White House has previously made similar statements, the call came hours before Trump hosts Chinese President Xi for a two-day summit at his Mar-a-Lago estate in Florida.
Pyongyang is on a quest to develop a long-range missile capable of hitting the U.S. mainland with a nuclear warhead, and has so far staged five nuclear tests, two of them previous year. But unlike the KN-15, which uses solid fuel, the missile fired Wednesday used liquid fuel and was sacked from a fixed location, rather than a mobile launcher, the official said. "The United States has moved on and is now trying to resolve problem through a larger scale, such as the summit with China shows".
Even before the missile test, North Korea's nuclear program was expected to be an important talking point between Xi and Trump. Earlier in March, North Korea fired four ballistic missiles that flew about 1,000 kilometres with three of them landing in waters that Japan claims as its exclusive economic zone.
"While pointing to the failure of the previous USA administrations to resolve the North Korean nuclear issue, the official said North Korea is a matter of urgent interest for the president and the administration as a whole".
"U.S. Pacific Command detected and tracked what we assess was a North Korean missile launch at 11:42 a.m. Hawaii time April 4", said Commander David Benham, a spokesman for U.S. Pacific Command, in a statement. "He is making it clear that, no matter what North Korea does, the United States won't commit to direct negotiations unless Pyongyang shows real willingness for disarmament".
The launch came amid worries that North Korea might soon conduct banned nuclear or long-range rocket tests.